The present invention relates to R.F. communications frequency spectrum management. Specifically, in the art of personal communications, an apparatus and method are provided to permit efficient use of a common channel by a plurality of local users while avoiding interference between users.
The R.F. communications spectrum is managed under current law to provide the equitable use of the radio frequency spectrum for members of the public. Current regulations for local geographic users permit the use of a single channel of the communications radio spectrum by multiple parties. This therefore requires time limitations now set to be two minutes, on users assigned to a common frequency, and a brief waiting period is imposed before using the frequency to be certain the channel is clear before a user commences transmission.
Two way digital radio has also been used to provide communications between a base station and plurality of subservient or "slave" stations. A controller at each base station is used to determine when a base station may commence transmission. The base station interrogates or "polls" each subsidiary station when the channel is clear thus determining whether a signal is to be sent. The polling, however, takes up channel time which is wasted if the polled stations do not have traffic to send.
The use of digital communications in local geographic areas among users of a common channel holds the promise of permitting a more efficient use of the commonly shared communications channels. Transmitters and receivers can be arranged which transmit a digital message of fixed length which when received is decoded and displayed. Proposals of this type which rather than using voice communications utilize digital messages arranged in packets for transmission are more completely set forth in a study conducted under contract to the Federal Communications Commission, FCC contract number 188, December 1976, "A study of Digital uses and Standards for Land/mobile channels" by Sachs/Freeman Associates, Inc.
The present invention will provide management of a communications channel which implements the digital communication concepts embodied in the study.